Efficient regeneration of dragon fruit (Hylocereus undatus) and an assessment of the genetic fidelity of in vitro-derived plants using ISSR markers

Dragon fruit (Hylocereus undatus) is a popular fruit crop in southern China. To meet the increasing demand of consumers and the industry, an efficient regeneration system via organogenesis was established for the rapid propagation of red-type dragon fruit ('Zihonglong'). Young nodes (30 60 mm in length) were collected in the Spring from mature plants, and new shoots were generated from the areoles on Murashige and Skoog (MS) basal medium supplemented with 0.5 mu M gibberellic acid (GA(3)). The best medium for in vitro micropropagation was solid 1.0x MS medium containing 2.0 mu M 6-benzyladenine (BA) and 0.5 mu M alpha-naphthaleneacetic acid (NAA). The highest proliferation ratio (8.2) and the most vigorous shoots were attained in 1 month on this medium. Well-developed shoots were then transferred into liquid 0.5 x MS medium containing 1.0 mu M NAA, in which perlite was used instead of agar for rhizogenesis. The rooting percentage reached 100%, and approx. six-to-ten white roots, each 5 8 cm in length, were obtained from each shoot in 3 weeks. The rooted plantlets were washed in tap water and transferred to pots containing a 1:1 (v/v) mixture of soil and sand for acclimatisation. To detect any somaclonal variation among in vitro-derived shoots, a total of 442 Inter-Simple Sequence Repeat (ISSR) markers, generated using 66 PCR primers, were assayed. No polymorphic markers were detected among the 47 in vitro-derived shoots selected at random after 15 sub-cultures, indicating a high level of genetic fidelity in the shoots generated using the regeneration method described here.